IB/mlx4: Sanity check userspace send queue sizes

Add sanity checks to send queue sizes passed in from userspace. The
minimum sq stride value below is taken from the MT25408 PRM (section
11.10, Table 306, log_sq_stride definition).

Without this check, userspace can submit arbitrarily large/small
values for the number of WQEs and the stride, which can crash the
kernel.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>